1. Field of the Invention
This invention relates to lubricant base stocks, which can also serve as complete lubricants in some cases; compounded lubricants, which include at least one additive for such purposes as improving high pressure and/or wear resistance, corrosion inhibition, and the like along with the lubricant base stocks which contribute the primary lubricity to the compounded lubricants; refrigerant working fluids including lubricants according to the invention along with primary heat transfer fluids, and methods for using these materials. The lubricants and lubricant base stocks are generally suitable for use with most or all halocarbon refrigerants and are particularly suitable for use with substantially chlorine-free, fluoro-group-containing organic refrigerating heat transfer fluids such as pentafluoroethane, 1,1-difluoroethane, 1,1,1-trifluroethane, and tetrafluoroethanes, most particularly 1,1,1,2-tetrafluoroethane. The lubricants and base stocks, in combination with these heat transfer fluids, are particularly suitable for lubricating compressors that operate at least part of the time at temperatures substantially higher than those at which humans can be comfortable; such compressors are generally used, for example, in vehicle air conditioning.
2. Statement of Related Art
Chlorine-free heat transfer fluids are desirable for use in refrigerant systems, because their escape into the atmosphere causes less damage to the environment than the currently most commonly used chlorofluorocarbon heat transfer fluids such as trichlorofluoromethane and dichlorodifluoromethane. The widespread commercial use of chlorine-free refrigerant heat transfer fluids has been hindered, however, by the lack of commercially adequate lubricants. This is particularly true for one of the most desirable working fluids, 1,1,1,2-tetrafluoroethane, commonly known in the art as "Refrigerant 134a" or simply "R134a". Other fluoro-substituted ethanes are also desirable working fluids.
Before the change to substantially chlorine-free halocarbon refrigerants that was legally mandated during the last few years as a result of concern about the effect on chlorine containing emissions in harming the earth's ozone layer, it was conventional to use mineral oil lubricants for compressors of this type. Because of the design of many vehicle air conditioners, it has been found to be impossible to flush the former chlorine containing refrigerant heat transfer fluids and their associated mineral oil lubricants from the air conditioning equipment in these vehicles thoroughly. Instead, only drainage of the former fluids from the air conditioning equipment is possible, and such drainage can easily result in as much as 25% of the formerly used mineral oil lubricant remaining behind in the equipment when it is retrofitted with a chlorine free heat transfer fluid and lubricants suitable for use with such heat transfer fluids.
Esters of hindered polyols, which are defined for this purpose as organic molecules containing at least five carbon atoms, at least 2 --OH groups, and no hydrogen atoms on any carbon atom directly attached to a carbon atom bearing an --OH group, have already been recognized in the art as high quality lubricant base-stocks for almost any type of refrigeration machinery employing a fluorocarbon refrigerant, particularly one free from chlorine. However, room for improvement in the art still exists.